1. Field of the Invention
The present invention is generally in the field of electronic circuits and systems. More specifically, the present invention is in the field of amplifier circuitry.
2. Background Art
Audio amplifiers often form an integral part of mobile devices such as cellular telephones. For example, an audio amplifier may boost a low amplitude input signal into an output signal that drives a cellular telephone headset or other load. However, audio amplifiers face at least two problems when used in mobile devices.
First, conventional audio amplifiers are often unable to coherently address an ON/OFF transient, known as a pop/click, audio interference that occurs when a mobile device is powered ON or OFF. Conventional audio amplifiers that use large passive components to limit transient noises are often expensive or difficult to integrate with driver circuitry. Similarly, conventional audio amplifiers that shift an ON/OFF transient to an inaudible frequency using a ramp signal generator are not easily compatible with ground referenced headset drivers. Largely, conventional audio amplifiers have been unable to cost-effectively reduce the ON/OFF transients that often degrade the performance of mobile devices.
Second, conventional audio amplifiers are typically unable to cost-effectively couple the driver circuitry that resides on a driver chip to the communications circuitry that is integrated into a distinct chip, such as a transceiver baseband chip. Unfortunately, conventional audio amplifiers that utilize alternating current (AC) coupling capacitors to provide a direct current (DC) offset may add cost and increase printed circuit board space. Conventional audio amplifiers using AC coupling capacitors may also distort the frequency response and other operating parameters of a mobile device.
Accordingly, there is a need to overcome the drawbacks and deficiencies in the art by providing an amplifier with reduced ON/OFF transient and offset compensation, and which is suitable for implementation in a mobile communications device. Furthermore, it is desirable that the amplifier can be implemented to include variable amplifier gain and multi-point offset compensation.